Fruit Set

The Role of Fruit Set in the Annual Life Cycle of the Vine

The percentage of grapes that will develop from their embryonic state varies roughly between 25% and 65%. Varietal type largely determines how many grapes will be in each cluster. Spraying for pests, fertilizing and pruning often continue during fruit set.

The vine needs sufficient carbohydrates to properly complete the process. Poor fruit set usually manifests millerandage or coulure. Millerandage occurs when the temperatures are too cold, or there is too much rain during fruit set. The berries develop irregularly and the yield is reduced.

Coulure is French for “shatter” and occurs when the grapes are not properly pollinated. The fruit development is stifled and the small berries they eventually fall off of the vine. Merlot, Grenache and Malbec are all particularly susceptible to coulure.

If the vine is starved for energy, it will not develop many viable berries and will grow excessive foliage instead. Too much nitrogen in the soil from excessive rainfall is usually to blame for these conditions.

Vines are rarely irrigated right before fruit set except in a few arid regions. Young shoots are often cut back in the weeks before fruit set so the vine will concentrate all of its energy on the process.